Base station apparatus, method, and radio communication system

ABSTRACT

A mobile communications terminal divides a plurality of multipath signals associated with radio signals transmitted from a plurality of base stations using an S-CCPCH into groups by base station, i.e., by transmit source, maximum-ratio-combines a plurality of multipath signals associated with each same base station which is a transmit source into a composite signal, decodes the composite signal, and selects a composite signal having a good decoded result from among decoded composite signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/652,391, filed Jan. 5, 2010, which is a divisional application ofU.S. application Ser. No. 10/582,955, filed Jun. 15, 2006, which is theNational Stage of International Application No. PCT/JP04/04502, filedMar. 30, 2004. The entire contents of U.S. application Ser. Nos.12/652,391 and Ser. No. 10/582,955 are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a mobile communications terminal and aradio communications system which, when receiving multimedia datatransmitted from a base station using a CDMA (Code Division MultipleAccess) method, can improve the reception quality of the multimediadata.

BACKGROUND OF THE INVENTION

Related art radio communications systems are based on the premise thatthere is a one-to-one correspondence between base stations and mobilecommunications terminals (e.g., mobile phones and mobile PCs), andtherefore do not support services of transmitting data to two or moremobile communications terminals simultaneously using a base station.There is a previously known method of notifying broadcast informationfrom a base station to all mobile communications terminals in thecontrol area of the base station all at once using a common channel.However, this method is aimed at notifying information about control toall mobile communications terminals in the control area all at once, butis not aimed at transmitting data, such as audio data and image data, toall mobile communications terminals in the control area all at once.

In recent years, expectations have been running high for the use ofmultimedia services as mobile communications services. Particularly, thespotlight has been turned on a technology of simultaneously deliveringmultimedia data about sports live broadcasting, weather report, andradio, etc. to two or more mobile communications terminals.

There has been proposed a technology of, in addition to a first commonchannel (P-CCPCH: Primary-Common Control Physical Channel) which a basestation uses when notifying broadcast information to two or more mobilecommunications terminals, providing a second common channel (S-CCPCH:Secondary-Common Control Physical Channel) which the base station useswhen delivering signaling or multimedia data to two or more mobilecommunications terminals, and delivering multimedia data from the basestation to two or more mobile communications terminals using the S-CCPCH(see patent reference 1 and nonpatent reference 1).

By thus delivering multimedia data using an S-CCPCH, a base station cansimultaneously provide multimedia data to two or more mobilecommunications terminals. However, when a mobile communications terminalis located in the vicinity of the periphery of the control area of thebase station, the electric wave transmitted from the base station maybecome weak and hence the reception quality of the electric wave maydegrade even if the mobile communications terminal is staying in thecontrol area of the base station.

To solve this problem, the base station has a function of controllingits transmission power so that the mobile communications terminal whichhas the smallest reception power in all the mobile communicationsterminals which are staying in the control area thereof will havereception power exceeding reference power.

On the other hand, each mobile communications terminal has a functionof, when receiving the same multimedia data from two or more basestations, improving the reception quality by maximum-ratio-combining thetwo or more multimedia data.

However, since the propagation paths of two or more multimedia data fromtwo or more base stations to each mobile communications terminal differfrom one another, the receipt times when each mobile communicationsterminal receives the two or more multimedia data transmitted from thetwo or more base stations differ from one another, and therefore eachmobile communications terminal cannot carry out maximum ratio combiningof the two or more multimedia data if the receipt time differencebecomes beyond a predetermined time period.

[Patent reference 1] JP, 2003-188818,A

[Nonpatent reference 1] 3GPP Standardization Document R1-031103Selective Combining for MBMS

A problem with related art radio communications systems constructed asmentioned above is that while a base station can secure the receptionquality of each mobile communications terminal staying in the controlarea thereof by controlling its transmission power so that the mobilecommunications terminal which has the smallest reception power in allthe mobile communications terminals which are staying in the controlarea thereof will have reception power exceeding reference power, anincreasing of the transmission power assigned to the S-CCPCH may degradethe reception quality of information transmitted to a mobilecommunications terminal using another channel since the transmissionpower assigned to the other channel becomes low relatively.

Another problem is that while if each mobile communications terminalmaximum-ratio-combines the same multimedia data transmitted from two ormore base stations, each mobile communications terminal can improve thereception quality of the multimedia data without each base stationcontrolling its transmission power, since the propagation paths of twoor more multimedia data from the two or more base stations to eachmobile communications terminal differ from one another, the receipttimes when each mobile communications terminal receives the two or moremultimedia data transmitted from the two or more base stations differfrom one another, and therefore each mobile communications terminalcannot carry out maximum ratio combining of the two or more multimediadata if the receipt time difference becomes beyond a predetermined timeperiod.

The present invention is made in order to solve the above-mentionedproblems, and it is therefore an object of the present invention toprovide a mobile communications terminal and a radio communicationssystem which can improve the reception quality of multimedia datawithout controlling the power required for transmission of themultimedia data by means of a base station.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided a mobilecommunications terminal including: a maximum-ratio-combining means fordividing a plurality of multipath signals associated with radio signalstransmitted from a plurality of base stations using a common channelinto groups by base station, i.e., by transmit source, and formaximum-ratio-combining a plurality of multipath signals associated witheach same base station which is a transmit source into a compositesignal; and a decoding means for decoding the composite signal outputtedfrom the maximum-ratio-combining means, the mobile communicationsterminal selecting a composite signal having a good decoded result fromamong composite signals decoded by the decoding means.

In accordance with the present invention, there is also provided amobile station which can receive a multimedia broadcast multicastservice (MBMS) of multicasting or broadcasting a multimedia data to aplurality of mobile stations in a communications system, said mobilestation comprising: a power ratio receiving unit for receivinginformation about a power ratio between a power of a common controlphysical channel used for multicasting or broadcasting said multimediadata in each of given cells and a power of a common pilot channel usedfor transmitting an information on reference of timing in each of thegiven cells; a service information receiving unit of receiving serviceinformation indicating a state of an MBMS service in each of the givencells; a cell selecting unit of acquiring a set including a plurality ofcells from which a mobile station can receive an MBMS on the basis ofthe information about said power ratio which is received by said powerratio receiving unit, and said service information received by saidservice information receiving unit; and a ranking unit for ranking theplurality of cells on the basis of the information about said powerratio in each of the given cells, which is received by said power ratioreceiving unit, and the power of said common pilot channel, and whereinsaid cell selecting unit determines the plurality of cells included insaid set on the basis of the ranking determined by said ranking unit anda predetermined threshold.

In accordance with the present invention, there is also provided a basestation which can be used for providing a multimedia broadcast multicastservice (MBMS) of multicasting or broadcasting a multimedia data to aplurality of mobile stations in a communications system, said basestation comprising: a power ratio transmitting unit for transmittinginformation about a power ratio between a power of a common controlphysical channel used for multicasting or broadcasting said multimediadata in each of given cells and a power of a common pilot channel usedfor transmitting an information on reference of timing in each of thegiven cells; and a service information transmitting unit fortransmitting service information indicating a state of an MBMS servicein said each of the given cells, wherein said base station transmits theinformation about said power ratio and said service information to saidmobile station in order to enable a mobile station which will receivethe information about said power ratio and said service information toacquire a set including a plurality of cells from which said mobilestation can receive an MBMS on the basis of the information about saidpower ratio and said service information, and in order to enable saidmobile station which will receive the information about said power ratioto determine a ranking of the plurality of cells on the basis of theinformation about said power ratio in each of the given cells and thepower of said common pilot channel, and to enable the mobile station todetermine the plurality of cells included in said set on the basis ofthe determined ranking and a predetermined threshold, said base stationtransmits the information about said power ratio in each of the givencells to said mobile station.

Therefore, the present invention offers an advantage of being able toimprove the reception quality of the radio signals without each basestation controlling its transmission power.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram showing a radio communications system inaccordance with embodiment 1 of the present invention;

FIG. 2 is a block diagram showing a mobile communications terminal inaccordance with embodiment 1 of the present invention;

FIG. 3 is a block diagram showing a base station in accordance withembodiment 1 of the present invention;

FIG. 4 is a block diagram showing a base station control apparatus inaccordance with embodiment 1 of the present invention;

FIG. 5 is an explanatory diagram showing the configuration of channelsbetween a mobile communications terminal and a base station;

FIG. 6 is an explanatory diagram showing a base station to be monitored;

FIG. 7 is a flow chart showing processing carried out by the mobilecommunications terminal in accordance with embodiment 1 of the presentinvention;

FIG. 8 is a flow chart showing the processing carried out by the mobilecommunications terminal in accordance with embodiment 1 of the presentinvention;

FIG. 9 is a flow chart showing processing carried out by a mobilecommunications terminal in accordance with embodiment 2 of the presentinvention;

FIG. 10 is a flow chart showing processing carried out by a mobilecommunications terminal in accordance with embodiment 3 of the presentinvention;

FIG. 11 is a flow chart showing the processing carried out by a mobilecommunications terminal in accordance with embodiment 3 of the presentinvention;

FIG. 12 is a sequence diagram showing signaling for updating of anactive set in a radio communications system;

FIG. 13 is a sequence diagram showing parameter information at the timeof the updating of the active set in the radio communications system;

FIG. 14 is a flow chart showing a process of updating the active set ina mobile communications terminal;

FIG. 15 is a sequence diagram showing notification of the ratio betweenthe power of a CPICH and that of an S-CCPCH; and

FIG. 16 is a flow chart showing a process of updating the active set ina mobile communications terminal.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereafter, in order to explain this invention in greater detail, thepreferred embodiments of the present invention will be described withreference to the accompanying drawings.

Embodiment 1

FIG. 1 is a block diagram showing a radio communications system inaccordance with embodiment 1 of the present invention, and, in thefigure, a service center 1 stores contents for delivery and delivers thecontents. A GGSN (Gateway GPRS Support Node) 2 is a gate with anexternal network (e.g., the Internet network) which serves as a gatewaywith the outside of the radio communications system, and secures a path(path) via which packets are passed. The GGSN also carries out processesincluding collection of accounting information, mobility management, QoS(Quality of Service) negotiation, and policy control for adjustingtraffic. An SGSN (Service GPRS Support Node) 3 takes charge of packetcommunications, and deals with authentication about each user, servicesubscription, routing, management of mobility, service restrictions,context storage, accounting information, etc.

Each base station control apparatus 4 is connected to the SGSN 3, andhas a function of relaying between the core network and radio channelswith base stations 5. Each base station control apparatus 4 mainlymanages radio resources, and provides an instruction for establishing orreleasing a channel with a base station 5. Each base station 5 deliversa radio signal (e.g., multimedia data or a pilot signal) to a mobilecommunications terminal 6 staying in a control area under the controlthereof using, for example, an S-CCPCH (or a common channel) accordingto an instruction from a base station control apparatus 4.

Each mobile communications terminal 6 has a function of, when receivingmultipath signals associated with radio signals transmitted from aplurality of base stations 5 using an S-CCPCH, dividing the multipathsignals into groups by base station 5, i.e., by transmit source,maximum-ratio-combining a plurality of multipath signals which aregrouped into each same base station 5, i.e., each same transmit sourceinto a composite signal, decoding the composite signal, and selecting adecoded composite signal having a good decoded result from decodedcomposite signals.

FIG. 2 is a block diagram showing each mobile communications terminal inaccordance with embodiment 1 of the present invention. In the figure, alow noise amplifier unit 12 amplifies a multipath signal which is a weakradio signal received by an antenna 11. A frequency converting unit 13converts the frequency of the multipath signal amplified by the lownoise amplifier unit 12 to output an RF (Radio Frequency) signal. An A/Dconverter 14 converts the RF signal outputted from the frequencyconverting unit 13, which is an analog signal, into a digital signal. Asignal receiving means includes the antenna 11, low noise amplifier unit12, frequency converting unit 13, and A/D converter 14.

When receiving an RF signal which is the digital signal from the A/Dconverter 14, a search unit 15 detects abase station 5 which is thetransmit source of the multipath signal by carrying out cell searchprocessing. A code generator 16 generates a scrambling codecorresponding to the base station 5 detected by the search unit 15.

When base stations A and B which are included in the plurality of basestations 5 are set to be base stations 5 to be monitored (referred to asan active set from here on), a finger assignment control unit 17controls an RAKE combining unit 18 so that an RF signal (referred to asan RF signal A-1 from there on) associated with a first multipath signaltransmitted from the base station A is assigned to a finger unit 18 a,an RF signal (referred to as an RF signal A-2 from here on) associatedwith a second multipath signal transmitted from the base station A isassigned to a finger unit 18 b, an RF signal (referred to as an RFsignal B-1 from here on) associated with a first multipath signaltransmitted from the base station B is assigned to a finger unit 18 c,and an RF signal (referred to as an RF signal B-2 from here on)associated with a second multipath signal transmitted from the basestation B is assigned to a finger unit 18 d.

A cell combining unit 18 e of the RAKE combining unit 18maximum-ratio-combines the RF signal A-1 assigned to the finger unit 18a and the RF signal A-2 assigned to the finger unit 18 b into acomposite signal, and stores the composite signal in a cell input memory19 a. A cell combining unit 18 f maximum-ratio-combines the RF signalB-1 assigned to the finger unit 18 c and the RF signal B-2 assigned tofinger unit 18 d into a composite signal, and stores the compositesignal in a cell input memory 19 b.

A maximum-ratio-combining means includes the search unit 15, codegenerator 16, finger assignment control unit 17, RAKE combining unit 18,and cell input memories 19 a and 19 b.

A decoding unit 20 decodes the composite signal stored in the cell inputmemory 19 a and stores the decoded composite signal in a cell outputmemory 21 a, and also decodes the composite signal stored in the cellinput memory 19 b and stores the decoded composite signal in a celloutput memory 21 b. A decoding means includes the decoding unit 20 andcell output memories 21 a and 21 b.

A selecting unit 22 selects a composite signal having a good decodedresult from the decoded composite signals stored in the cell outputmemories 21 a and 21 b, and outputs the selected composite signal to adownlink common channel receiving unit 23. The selecting unit 23constitutes a selecting means.

The downlink common channel receiving unit 23 outputs the selectedcomposite signal outputted from the selecting unit 22 to a protocolprocessing unit 26 when the composite signal is control information,whereas it outputs the composite signal to an application processingunit 27 when the composite signal is application data. Since theselecting unit 22 does not carry out the process of selecting acomposite signal when the decoded composite signal stored in the celloutput memory 21 a is broadcast information, a broadcast informationreceiving unit 24 receives the composite signal stored in the celloutput memory 21 a and outputs it to the protocol processing unit 26.

Since the selecting unit 22 does not carry out the process of selectinga composite signal when the decoded composite signal stored in the celloutput memory 21 a is application data or control information and hasbeen transmitted to the mobile communications terminal by a base station5 using a downlink dedicated channel, a downlink dedicated channelreceiving unit 25 receives the composite signal stored in the celloutput memory 21 a and outputs the composite signal to the applicationprocessing unit 27 when the composite signal is application data,whereas it outputs the composite signal to the protocol processing unit26 when the composite signal is control information.

The protocol processing unit 26 carries out processes aboutcommunications control, such as establishment or release of a channel,or handover, according to the composite signal (control information orbroadcast information) outputted from the downlink common channelreceiving unit 23, broadcast information receiving unit 24, or downlinkdedicated channel receiving unit 25.

The application processing unit 27 carries out transform processes, suchas voice codec and image codec according to the composite signal(application data) outputted from the downlink common channel receivingunit 23 or downlink dedicated channel receiving unit 25, and alsocarries out processes associated with man machine interfaces, such as akey input and a screen display.

An uplink common channel transmitting unit 28 carries out common channelprocesses, such as channel coding and transmission timing, whenreceiving control information outputted from the protocol processingunit 26. An uplink dedicated channel transmitting unit 29 carries outdedicated channel processes such as channel coding and transmissiontiming, when receiving a telephone number or the like outputted from theapplication processing unit 27.

A code generator 30 generates a spread code and a modulating unit 31performs spread modulation on a signal outputted from the uplink commonchannel transmitting unit 28 or uplink dedicated channel transmittingunit 29 using the above-mentioned spread code.

A D/A converter 32 converts the modulated signal outputted from themodulating unit 31, which is a digital signal, into an analog signal. Afrequency converting unit 33 converts the frequency of the modulatedsignal on which the D/A conversion is performed by the D/A converter 32to output an RF signal. A power amplifying unit 34 amplifies the powerof the RF signal, and outputs it to the antenna 11.

FIG. 3 is a block diagram showing each base station in accordance withembodiment 1 of the present invention. In the figure, when receivingbroadcast information from a corresponding base station controlapparatus 4, a broadcast information transmitting unit 41 performs acoding process of putting the broadcast information onto a P-CCPCH. Whenreceiving data or control information to be transmitted using adedicated channel (DPCH: Dedicated Physical channel), which istransmitted from the corresponding base station control apparatus 4, adownlink dedicated channel transmitting unit 42 performs a codingprocess of putting the data or control information onto the DPCH. Whenreceiving control information or multimedia data to be transmitted usingan S-CCPCH, which is transmitted from the corresponding base stationcontrol apparatus 4, a downlink common channel transmitting unit 43performs a coding process of putting the control information ormultimedia data onto the S-CCPCH.

A downlink code generator 44 generates a channelization code and ascrambling code for downlinks. A modulating unit 45 performs spreadmodulation on a signal outputted from the broadcast informationtransmitting unit 41, downlink dedicated channel transmitting unit 42,or downlink common channel transmitting unit 43 using the codes fordownlinks generated by the code generator 44.

A D/A converter 46 converts the modulated signal outputted from themodulating unit 45, which is a digital signal, into an analog signal. Afrequency converting unit 47 converts the frequency of the modulatedsignal on which D/A conversion is performed by the D/A converter 46 tooutput an RF signal. A power amplifying unit 48 amplifies the power ofthe RF signal, and outputs it to an antenna 49.

When the antenna 49 receives a weak radio signal transmitted from amobile communications terminal 6, a low noise amplifier unit 50amplifies the radio signal. A frequency converting unit 51 converts thefrequency of the radio signal amplified by the low noise amplifier unit50 to output an RF signal. An A/D converter 52 converts the RF signaloutputted from the frequency converting unit 51, which is an analogsignal, into a digital signal.

An uplink code generator 53 generates a channelization code and ascrambling code for uplinks. A demodulating unit 54 demodulates the RFsignal outputted from the A/D converter 52 using the scrambling code foruplinks which is generated by the code generator 53, and alsodemultiplexes the demodulated RF signal into channel-by-channel signalsusing the channelization code for uplinks which is generated by the codegenerator 53. An uplink dedicated channel receiving unit 55channel-decodes a signal associated with each channel and transmits itto the corresponding base station control apparatus 4. An uplink commonchannel receiving unit 56 channel-decodes a signal associated with acommon channel (RACH: Random Access Channel), and transmits it to thecorresponding base station control apparatus 4.

FIG. 4 is a block diagram showing each base control apparatus inaccordance with embodiment 1 of the present invention. In the figure, atransmit-receive processing unit 61 for core network carries outcommunications protocol processes, such as a process about a protocolfor use with the core network, such as RANAP (Radio Access NetworkApplication Protocol), and a process about a protocol for use with otherbase control apparatus, such as RNSAP (Radio Network SubsystemApplication Part).

A QoS parameter mapping unit 62 acquires parameters of radio channelswhich satisfy requirements according to a QoS instruction from the corenetwork. A radio resource control unit 63 carries out a process aboutradio resources, and also carries out control of mobile communicationsterminals 6 and notification of parameters using RRC signaling. Aradio-link control unit 64 carries out buffering and control ofretransmission of data via a radio link.

A transmit-receive processing unit 65 for base station carries outcommunications protocol processes such as a process about a protocol foruse with base stations (Node-B), such as NBAP (NodeB Application Part).

However, how the functions of each base station control apparatus 4 areshared among the components is determined on the basis of its logicalfunctions, and they are not necessarily separated clearly when they areactually implemented via hardware or software.

FIG. 5 is an explanatory diagram showing the configuration of channelsdisposed between each mobile communications terminal 6 and each basestation 5. In the example of FIG. 5, the configuration of channels inthe case of using a W-CDMA method is shown. However, in actual fact,there is a possibility that a plurality of channels are used with themsharing a single channel.

First, a downlink physical channel from each base station 5 to eachmobile communications terminal 6 will be explained.

A CPICH (Common Pilot Channel) which each base station uses wheninforming a reference of timing, and a P-CCPCH (Primary-Common ControlPhysical Channel) which each base station uses when notifying otherbroadcast information are disposed for all mobile communicationsterminals 6 which are staying in a control area under the control ofeach base station 5. The P-CCPCH is used as a channel BCH for broadcastinformation (Broadcast channel).

An S-CCPCH (Secondary-Common Control Physical Channel) which each basestation 5 uses when transmitting signaling or data to each mobilecommunications terminal 6 is provided from each base station 5 to eachmobile communications terminal 6. A plurality of S-CCPCHs can beprovided.

A PICH (Paging Indicator channel) is provided as an indicator fordownlink paging.

Next, uplink channels from each mobile communications terminal 6 to eachbase station 5 will be explained.

There is provided an RACH (Random Access Channel) as a common channel,and there is also provided, as each of uplink and downlink channels, aDPCH (Dedicated Physical Channel) which is individually established wheneach base station communicates with a specific mobile communicationsterminal 6. The DPCH is established as each of the uplink and downlinkchannels, and is used for communications of voice data, data, etc., orsignaling by an upper layer. The DPCH can be divided into a DPDCH(Dedicated Physical Data Channel) which is a portion via which data aretransmitted, and a DPCCH (Dedicated Physical Control Channel) which is aportion via which bits about control are transmitted.

The DPCH is called a dedicated channel since it is used by an individualterminal, while other channels are called common channels since each ofthem is used in common by two or more terminals.

Next, the operation of the radio communications system in accordancewith this embodiment of the present invention will be explained.

First, the GGSN 2 extracts multimedia data about contents currentlybeing stored in the service center 1, and then transmits the multimediadata to the SGSN 3.

When receiving the multimedia data from the GGSN 2, the SGSN 3 searchesfor one or more mobile communications terminals 6 which use the serviceof delivering the contents, and transmits the multimedia data about thecontents in question to base station control apparatus 4 connected withbase stations 5 which are accommodating those mobile communicationsterminals 6.

When receiving the multimedia data from the SGSN 3, each base stationcontrol apparatus 4 controls base stations 5 so that each of themdelivers the multimedia data to target mobile communications terminalsusing the S-CCPCH.

Each target mobile communications terminal 6 receives the multimediadata delivered from one of the plurality of base stations 5 using theS-CCPCH.

However, when each target mobile communications terminal 6 is staying inthe vicinity of the periphery of a control area under the control of abase station 5 which has delivered the multimedia data thereto, forexample, the electric wave transmitted from the base station 5 maybecome weak and therefore the reception quality of the electric wave maydegrade even if each mobile communications terminal 6 is staying in thecontrol area.

The reason why the reception quality of the S-CCPCH channel degradeswhen each mobile communications terminal is staying in the periphery ofthe control area under the control of the base station which hasdelivered the multimedia data thereto is as follows. For the sake ofsimplicity, assume that abase station control apparatus 4 is connectedto abase station A and a base station B, and a mobile communicationsterminal 6 is staying in the vicinity of the periphery of the controlarea under the control of the base station A, as shown in FIG. 6.

In this case, since the distance between the mobile communicationsterminal 6 and the base station B is relatively short, a DPCH which is adedicated channel is established between the mobile communicationsterminal 6 and the base station A, and may be also established betweenthe mobile communications terminal 6 and the base station B.

When a DPCH is established between the mobile communications terminal 6and each of the base stations A and B, the mobile communicationsterminal 6 can receive data transmitted from each of the base stations Aand B using the DPCH, and can improve the reception quality of the databy maximum-ratio-combining both of the data from the base stations A andB.

However, since the S-CCPCH associated with the base stations A and Bwhich are common channels are established between the mobilecommunications terminal 6 and the base stations A and B, respectively,the mobile communications terminal 6 cannot carry out themaximum-ratio-combining of both of the data transmitted from the basestations A and B, and this results in the degradation in the receptionquality of the data.

Therefore, in order to improve the reception quality of the S-CCPCH, thebase station 5 only has to transmit the data by increasing the powerwhich is assigned to the S-CCPCH. However, the reception quality ofinformation transmitted using another channel may degrade since thetransmission power assigned to the other channel becomes low relativelywhen the base station 5 increases the power which is assigned to theS-CCPCH, as mentioned above,

In contrast, in accordance with this embodiment 1, each mobilecommunications terminal 6 is so constructed as shown in FIG. 2 in orderto improve the reception quality of the S-CCPCH without each basestation 5 increasing the power which is assigned to the S-CCPCH.

Hereafter, the operation of each mobile communications terminal 6 ofFIG. 2 will be explained. FIGS. 7 and 8 are flow charts showingprocessing carried out by each mobile communications terminal inaccordance with embodiment 1 of the present invention.

Although each mobile communications terminal 6 may be able to receiveradio signals transmitted from three or more base stations 5 using theS-CCPCH, assume that since restrictions are placed on the hardware ofthe receive part of each mobile communications terminal 6, each mobilecommunications terminal 6 selects, as the target to be monitored, notall of the base stations 5, but monitors only base stations 5 each ofwhich stands a good chance of increasing the reception quality of theradio signal (i.e., base stations 5 each of which provides a highpossibility that the reception quality is improved). In this case, asshown in FIG. 6, the mobile communications terminal 6 selects the basestations A and B as the target to be monitored and receives the radiosignals transmitted from the base stations A and B. However, since theradio signals reach the mobile communications terminal 6 after passingthrough various paths from the base stations A and B, the radio signaltransmitted from each of the base stations A and B is received, as amultipath signal, by the mobile communications terminal 6 a number oftimes.

Although it can be considered that each of the two or more base stations5 does not transmit multimedia data all of a sudden, but transmits apilot signals as a radio signal when no S-CCPCH is established betweeneach of them and the mobile communications terminal 6, each of the twoor more base stations 5 can transmit multimedia data to the mobilecommunications terminal 6 all of a sudden.

First, when the antenna 11 receives a multipath signal which is a radiosignal transmitted from the base station A or B, the low noise amplifierunit 12 of the mobile communications terminal 6 amplifies the multipathsignal.

When the low noise amplifier unit 12 amplifies the multipath signal, thefrequency converting unit 13 converts the frequency of the multipathsignal to generate and output an RF signal to the A/D converter 14.

When receiving the RF signal which is an analog signal from thefrequency converting unit 13, the A/D converter 14 carries outanalog-to-digital conversion of the RF signal to generate and output anRF signal which is a digital signal to both the RAKE combining unit 18and search unit 15.

When receiving the RF signal which is a digital signal from the A/Dconverter 14, the search unit 15 detects a base station 5 which is thetransmit source of the multipath signal in question by carrying out cellsearch processing. In other words, the search unit 15 checks to seewhether the multipath signal received by the antenna 11 has beentransmitted from either the base station A or the base station B.

To be more specific, since the multipath signal varies under theinfluence of fading as the mobile communications terminal 6 moves, thesearch unit 15 sets a code, timing, and so on for the S-CCPCH andsearches for the S-CCPCH (in step ST1), and calculates a delay profileand so on for the searched S-CCPCH (i.e., the S-CCPCH associated withthe base station A or S-CCPCH associated with the base station B) (instep ST2).

The finger assignment control unit 17 searches for the peak of the delayprofile calculated by the search unit 15, and controls the RAKEcombining unit 18 so that a multipath signal at the peak is assigned tothe finger unit of the RAKE combining unit 18 (in step ST3).

At this time, since the active set of base stations 5 to be monitoredincludes only the base stations A and B, when the transmit source of themultipath signal received by the antenna 11 is the base station A andthe RF signal outputted from the A/D converter 14 has not been assignedto the finger unit 18 a of the RAKE combining unit 18, the fingerassignment control unit 17 controls the RAKE combining unit 18 so thatthe RF signal (referred to as the RF signal A-1 from here on) isassigned to the finger unit 18 a.

In contrast, when the transmit source of the multipath signal receivedby the antenna 11 is the base station A and the RF signal outputted fromthe A/D converter 14 has been assigned to the finger unit 18 a of theRAKE combining unit 18, the finger assignment control unit 17 controlsthe RAKE combining unit 18 so that the RF signal (referred to as the RFsignal A-2 from here on) is assigned to the finger unit 18 b.

When the transmit source of the multipath signal received by the antenna11 is the base station B and the RF signal outputted from the A/Dconverter 14 has not been assigned to the finger unit 18 c of the RAKEcombining unit 18, the finger assignment control unit 17 controls theRAKE combining unit 18 so that the RF signal (referred to as the RFsignal B-1 from here on) is assigned to the finger unit 18 c.

In contrast, when the transmit source of the multipath signal receivedby the antenna 11 is the base station B and the RF signal outputted fromthe A/D converter 14 has been assigned to the finger unit 18 c of theRAKE combining unit 18, the finger assignment control unit 17 controlsthe RAKE combining unit 18 so that the RF signal (referred to as the RFsignal B-2 from here on) is assigned to the finger unit 18 d.

The code generator 16 generates a scrambling code corresponding to thebase station 5 detected by the search unit 15. For example, when thebase station 5 which is the transmit source of the multipath signal inquestion is the base station A, the code generator 16 generates ascrambling code corresponding to the base station A. In contrast, whenthe base station 5 which is the transmit source of the multipath signalin question is the base station B, the code generator 16 generates ascrambling code corresponding to the base station B.

When the finger units 18 a to 18 d of the RAKE combining unit 18 receivethe RF signals A-1, A-2, B-1, and B-2, respectively, they demodulatethem using the scrambling codes generated by the code generator 16,respectively.

When the RF signals A-1 and A-2 are assigned to the finger units 18 aand 18 b, respectively, the cell combining unit 18 e of the RAKEcombining unit 18 maximum-ratio-combines the RF signals A-1 and A-2 intoa composite signal (referred as a composite signal A), and stores thecomposite signal A in the cell input memory 19 a (in steps ST4 and ST5).

On the other hand, when the RF signals B-1 and B-2 are assigned to thefinger units 18 c and 18 d, respectively, the cell combining unit 18 fof the RAKE combining unit 18 maximum-ratio-combines the RF signals B-1and B-2 into a composite signal (referred as a composite signal B), andstores the composite signal B in the cell input memory 19 b (in stepsST4 and ST5).

When the cell combining unit 18 e of the RAKE combining unit 18 storesthe composite signal A in the cell input memory 19 a, the decoding unit20 decodes the composite signal A by performing turbo decode processingon the composite signal A (in steps ST11 and ST12), and stores thedecoded composite signal A in the cell output memory 21 a (in stepST13).

On the other hand, when the cell combining unit 18 f of the RAKEcombining unit 18 stores the composite signal B in the cell input memory19 b, the decoding unit 20 decodes the composite signal B by performingturbo decode processing on the composite signal B (in steps ST11 andST12), and stores the decoded composite signal B in the cell outputmemory 21 b (in step ST13).

The selecting unit 22 selects a composite signal having a good decodedresult from the decoded composite signals A and B respectively stored inthe cell output memories 21 a and 21 b, and outputs the selectedcomposite signal to the downlink common channel receiving unit 23.

For example, the selecting unit 22 checks the CRC results of the decodedcomposite signals A and B (in step ST14) so as to identify one of thecomposite signals having a normal CRC result.

The selecting unit 22 then selects the composite signal having a normalCRC result (in step ST15), and outputs the selected composite signal tothe downlink common channel receiving unit 23 (in step ST16).

When receiving the composite signal selected by the selecting unit 22,the downlink common channel receiving unit 23 outputs the selectedcomposite signal to the protocol processing unit 26 if the compositesignal is control information, whereas it outputs the selected compositesignal to the application processing unit 27 if the composite signal isapplication data.

When receiving the composite signal which is control information fromthe downlink common channel receiving unit 23, the protocol processingunit 26 carries out processing about communications control, such asestablishment or release of a channel, or handover, according to thecontrol information.

In other words, when the composite signal outputted from the downlinkcommon channel receiving unit 23 is associated with a multipath signaltransmitted from the base station A, the protocol processing unit 26carries out processing such as communications control processing forestablishing an S-CCPCH between the base station A and the mobilecommunications terminal, whereas when the composite signal outputtedfrom the downlink common channel receiving unit 23 is associated with amultipath signal transmitted from the base station B, the protocolprocessing unit 26 carries out processing such as communications controlprocessing for establishing an S-CCPCH between the base station B andthe mobile communications terminal.

After that, the search unit 15 searches for a plurality of multipathsignals associated with the S-CCPCH established by the protocolprocessing unit 26, the RAKE combining unit 18 maximum-ratio-combinesthe plurality of multipath signals searched for by the search unit 15into a composite signal, and the decoding unit 20 stores the compositesignal in the cell output memory 21 a.

When receiving the composite signal which is application data from thedownlink common channel receiving unit 23 after the S-CCPCH has beenestablished by the protocol processing unit 26 between the base stationA or B and the mobile communications terminal in the above-mentionedway, the application processing unit 27 carries out transformprocessing, such as voice codec and image codec, according to theapplication data.

Since the selecting unit 22 does not carry out the selection process ofselecting a composite signal when the decoded composite signal stored inthe cell output memory 21 a is broadcast information, the broadcastinformation receiving unit 24 receives the composite signal and outputsit to the protocol processing unit 26.

Since the selecting unit 22 does not carry out the process of selectinga composite signal when the decoded composite signal stored in the celloutput memory 21 a is application data or control information and hasbeen transmitted to the mobile communications terminal by the basestation 5 using a downlink dedicated channel, the downlink dedicatedchannel receiving unit 25 receives the composite signal stored in thecell output memory 21 a and outputs the composite signal to theapplication processing unit 27 when the composite signal is applicationdata, whereas it outputs the composite signal to the protocol processingunit 26 when the composite signal is control information.

As can be seen from the above description, each mobile communicationsterminal in accordance with this embodiment 1 divides a plurality ofmultipath signals associated with radio signals transmitted thereto by aplurality of base stations 5 using an S-CCPCH into groups by basestation, i.e., by transmit source, maximum-ratio-combines a plurality ofmultipath signals associated with each same base station 5, i.e., eachsame transmit source into a composite signal, decodes the compositesignal, and selects a composite signal having a good decoded result fromamong decoded composite signals. Therefore, the present embodimentoffers an advantage of being able to improve the reception quality ofradio signals without each base station 5 controlling its transmissionpower.

In accordance with this embodiment 1, the finger units 18 a and 18 b ofeach mobile communications terminal receive RF signals A-1 and A-2associated with a multipath signal transmitted from a base station A,respectively, and the finger units 18 c and 18 d of each mobilecommunications terminal receive RF signals B-1 and B-2 associated with amultipath signal transmitted from a base station B, respectively, aspreviously mentioned. As an alternative, RF signals can be arbitrarilyassigned to the finger unit 18 a to 18 d, respectively. For example, thefinger units 18 a, 18 b, and 18 c can receive the RF signals A-1 and A-2and an RF signal A-3 associated with the multipath signal transmittedfrom the base station A, respectively, and the finger unit 18 d canreceive the RF signal B-1 associated with the multipath signaltransmitted from the base station B.

In addition, in accordance with this embodiment 1, the RAKE combiningunit 18 includes the cell combining units 18 e and 18 f, as previouslymentioned. As an alternative, the RAKE combining unit 18 can includeonly one cell combining unit having the functions of the cell combiningunits 18 e and 18 f.

Furthermore, in general, the hardware of the decoding unit 20 has alarge circuit structure. Therefore, in accordance with this embodiment1, the decoding unit 20 carries out decode processing with timedivision, as previously mentioned. Needless to say the decoding unit 20can alternatively include two decoding units.

In addition, in accordance with this embodiment 1, each mobilecommunications terminal includes the two cell output memories 21 a and21 b, as well as the two cell input memory 19 a and 19 b, as previouslymentioned. Needless to say each mobile communications terminal canalternatively include only a cell output memory and only a single cellinput memory.

Embodiment 2

In accordance with above-mentioned embodiment 1, the selecting unit 22selects a composite signal having a good decoded result from decodedcomposite signal A and B respectively stored in the cell output memories21 a and 21 b, and outputs the selected composite signal to the downlinkcommon channel receiving unit 23, as previously mentioned. As analternative, the selecting unit 22 can check to see whether the decodedcomposite signal A stored in the cell output memory 21 a has a gooddecoded result, for example, as shown in FIG. 9, and, when determiningthat the decoded result is good, can output the decoded composite signalA to the downlink common channel receiving unit 23 without checking tosee whether the decoded composite signal B stored in the cell outputmemory 21 b has a good decoded result (in steps ST17 and ST18). Whendetermining that the decoded result of the decoded composite signal Astored in the cell output memory 21 a is not good, the selecting unit 22further checks to see whether or not the decoded result of the decodedcomposite signal B stored in the cell output memory 21 b is good, and,when determining that the decoded result is good, outputs the decodedcomposite signal B to the downlink common channel receiving unit 23.

In accordance with this embodiment 2, since the selecting unit does notneed to perform the process of checking to see whether or not otherdecoded results are good if determining that the previously-decodedresult is good, useless processings can be reduced.

Embodiment 3

In above-mentioned embodiment 1, the example in which the active setincludes only the base stations A and B is shown. There can be providedan update request means for comparing the reception levels of radiosignals transmitted from a plurality of base stations 5 with oneanother, and for transmitting a request to update the active setaccording to the result of the comparison.

The search unit 15 and protocol control unit 26 of FIG. 2 constitute theupdate request means.

FIGS. 10 and 11 are flow charts showing processing carried out by eachmobile communications terminal in accordance with embodiment 3 of thepresent invention.

Next, the operation of each mobile communications terminal in accordancewith this embodiment of the present invention will be explained.

A path loss (path loss) or CPICH Ec/No (energy-vs.-noise per one chip ofCPICH), CPICH-RSCP (CPICH Received Signal Code Power: power assigned tothe code of CPICH) can be defined as the reception level of a CPICH, forexample.

The search unit 15 acquires the reception level of the CPICH of eachbase station 5 which is not included in the current active set, as wellas the reception level of the CPICH of each base station 5 included inthe active set (in step ST21).

When acquiring these reception levels of the CPICHs of the base stations5, the search unit 15 then calculates an addition threshold Tadd (instep ST23) by ranking the reception levels of the CPICHs in order (instep ST22).

In other words, the search unit 15 sets the lowest one of the receptionlevels of the CPICHs of the base stations 5 included in the active setto X, and calculates an addition threshold Tadd from the lowest CPICHreception level X and a hysteresis parameter H for preventing variationsin the active set. In this case, the search unit 15 can receive theaddition threshold Tadd from an upper layer instead of calculating theaddition threshold Tadd.Tadd=X+H/2

The search unit 15 checks to see whether or not there is a receptionlevel which continues to exceed the above-mentioned addition thresholdTadd throughout a predetermined time period T (the time period T is atimer value for removing instant variations) in the reception levels ofthe CPICHs of the base stations 5 which are not included in the currentactive set (in step ST24).

When there is a reception level which continues to exceed theabove-mentioned addition threshold Tadd throughout the predeterminedtime period T in the reception levels of the CPICHs of the base stations5 which are not included in the current active set, the search unit 15examines whether a further base station can be accommodated in theactive set. In other words, the search unit 15 examines whether themobile communications terminal can bear the increase in the load ofcarrying out the receiving processing which is caused by the addition ofa base station 5 into the active set (in step ST25), and, whendetermining that a further base station can be accommodated in theactive set, determines that it will carry out a process of adding a basestation into the active set as will be mentioned below. In this case,the search unit 15 shifts to processing of a terminal A of FIG. 11.

On the other hand, when determining that any further base station cannotbe accommodated in the active set, the search unit 15 determines that itwill carryout a process of replacing a base station of the currentactive set with another base station as will be mentioned below. In thiscase, the search unit 15 shifts to processing of a terminal B of FIG.11.

When there is no reception level which continues to exceed the additionthreshold Tadd throughout the predetermined time period T in thereception levels of the CPICHs of the base stations 5 which are notincluded in the current active set, the search unit 15 calculates adeletion threshold Tdelete from both the lowest one X of the receptionlevels of the CPICHs of the base stations 5 included in the active set,and the hysteresis parameter H (in step ST26). As an alternative, thesearch unit 15 can receive the deletion threshold Tdelete from an upperlayer instead of calculating the deletion threshold Tdelete.Tdelete=X−H/2

The search unit 15 then checks to see whether or not there is areception level which continues to be lower than the above-mentioneddeletion threshold Tdelete throughout the predetermined time period T inthe reception levels of the CPICHs of the base stations 5 which areincluded in the current active set (in step ST24).

When there is a reception level which continues to be lower than thedeletion threshold Tdelete throughout the predetermined time period T inthe reception levels of the CPICHs of the base stations 5 which areincluded in the current active set, the search unit 15 determines thatit will carry out a process of deleting a corresponding base stationfrom the active set as will be mentioned below. In this case, the searchunit 15 shifts to processing of a terminal C of FIG. 11.

On the other hand, when there is no reception level which continues tobe lower than the deletion threshold Tdelete throughout thepredetermined time period T in the reception levels of the CPICHs of thebase stations 5 which are included in the current active set, the searchunit 15 ends the processing without carrying out the process of updatingthe active set.

The Process of Adding a Base Station into the Active Set

When the search unit 15 determines implementation of the process ofadding a base station to the active set, the protocol processing unit 26transmits addition request signaling indicating a request to add a basestation to the active set to a base station 5 (in step ST31).

In other words, the protocol processing unit 26 outputs the additionrequest signaling indicating a request to add a base station to theactive set to the uplink dedicated channel transmitting unit 29, and theuplink dedicated channel transmitting unit 29 carries out dedicatedchannel processing to outputs the addition request signaling to themodulating unit 31.

The modulating unit 31 performs spread modulation on the additionrequest signaling outputted from the uplink dedicated channeltransmitting unit 29 using a spread code generated by the code generator30.

The D/A converter 32 converts the modulated signal outputted from themodulating unit 31, which is a digital signal, into an analog signal,the frequency converting unit 33 converts the frequency of the modulatedsignal on which the digital-to-analog conversion is performed by the D/Aconverter 32 to generate and output an RF signal, and the poweramplifying unit 34 amplifies the power of the RF signal and outputs itto the antenna 11.

Thus, the addition request signaling indicating the request to add abase station to the active set is transmitted to a base station 5, andthe base station 5 transmits the addition request signaling to acorresponding base station control apparatus 4.

When the base station control apparatus 4 permits the addition of a basestation to the active set, the base station 5 transmits additionpermission signaling indicating permission to add a base station to theactive set (including the S-CCPCH parameters of the base station 5 whichis permitted to be newly added to the active set) to the mobilecommunications terminal 6 using a DPCH which is a dedicated channel.

When the antenna 11 receives the addition permission signaling which istransmitted from the base station 5, and the protocol processing unit 26of the mobile communications terminal 6 then receives the additionpermission signaling from the downlink dedicated channel receiving unit25 in the same way as previously mentioned in embodiment 1 (in stepST32), the protocol processing unit 26 determines whether or not theaddition of a base station to the active set has been permitted byanalyzing the addition permission signaling (in step ST33).

When determining that the addition of a base station to the active sethas been permitted, the protocol processing unit 26 refers to theS-CCPCH parameters included in the addition permission signalingindicating permission to add a base station to the active set, andidentifies the base station 5 which is to be added to the active set andthen adds the base station 5 to the active set (in step ST34).

The protocol processing unit 26 then notifies the S-CCPCH parameters tothe search unit 15, finger assignment control unit 17, and RAKEcombining unit 18.

After that, the mobile communications terminal starts a process ofreceiving data associated with the S-CCPCH of the base stations 5 of theactive set including the added base station 5 (in step ST35).

The Process of Replacing a Base Station of the Active Set with AnotherBase Station

When the search unit 15 determines implementation of the process ofreplacing a base station of the active set with another base station,the protocol processing unit 26 transmits replacement request signalingindicating a request to replace a base station of the active set withanother base station to a base station 5 in the same way that ittransmits addition request signaling indicating a request to add a basestation to the active set (in step ST41).

Thus, the replacement request signaling indicating a request to replaceabase station of the active set with another base station is transmittedto a base station 5, and the base station 5 transmits the replacementrequest signaling to a corresponding base station control apparatus 4.

When the base station control apparatus 4 permits the replacement of abase station of the active set with another base station, the basestation 5 transmits replacement permission signaling indicatingpermission to replace a base station of the active set with another basestation (including the S-CCPCH parameters of the other base station 5which is permitted to be newly added to the active set) to the mobilecommunications terminal 6 using a DPCH.

When the antenna 11 receives the replacement request signalingindicating a request to replace a base station of the active set withanother base station which is transmitted from the base station 5, andthe protocol processing unit 26 of the mobile communications terminal 6then receives the replacement request signaling from the downlinkdedicated channel receiving unit 25 in the same way as previouslymentioned in embodiment 1 (in step ST42), the protocol processing unit26 determines whether or not the replacement of a base station of theactive set with another base station has been permitted by analyzing thereplacement permission signaling (in step ST43).

When determining that the replacement of a base station of the activeset with another base station has been permitted, the protocolprocessing unit 26 excludes abase station 5 having the lowest receptionlevel from the base stations 5 included in the current active set (instep ST44).

The protocol processing unit 26 further refers to the S-CCPCH parametersincluded in the replacement permission signaling indicating permissionto replace a base station of the active set with another base station,and identifies the other base station 5 which is to be added to theactive set and then adds the other base station 5 to the active set (instep ST45).

The protocol processing unit 26 then notifies the S-CCPCH parameters tothe search unit 15, finger assignment control unit 17, and RAKEcombining unit 18.

After that, the mobile communications terminal starts a process ofreceiving data associated with the S-CCPCH of the base stations 5 of theactive set including the other base station 5 which is added to theactive set in place of the excluded base station (in step ST46).

The Process of Deleting a Base Station from the Active Set

When the search unit 15 determines that it will carry out implementationof the process of deleting a base station from the active set, theprotocol processing unit 26 transmits deletion request signalingindicating a request to delete a base station from the active set to abase station 5 in the same way that it transmits addition requestsignaling indicating a request to add a base station to the active set(in step ST51).

Thus, the deletion request signaling indicating a request to delete abase station from the active set is transmitted to a base station 5, andthe base station 5 transmits the deletion request signaling to acorresponding base station control apparatus 4.

When the base station control apparatus 4 permits the deletion of a basestation from the active set, the base station 5 transmits deletionpermission signaling indicating permission to delete a base station fromthe active set to the mobile communications terminal 6 using a DPCH.

When the antenna 11 receives the deletion permission signalingindicating a permission to delete a base station from the active setwhich is transmitted from the base station 5, and the protocolprocessing unit 26 of the mobile communications terminal 6 then receivesthe deletion permission signaling from the downlink dedicated channelreceiving unit 25 in the same way as previously mentioned in embodiment1 (in step ST52), the protocol processing unit 26 determines whether ornot the deletion of a base station from the active set has beenpermitted by analyzing the deletion permission signaling (in step ST53).

When determining that the deletion of a base station from the active sethas been permitted, the protocol processing unit 26 stops the process ofreceiving data associated with the S-CCPCH of a base station 5 havingthe lowest reception level which is included in the base stations 5 ofthe current active set (in step ST54), and excludes the base station 5having the lowest reception level from the current active set (in stepST55).

FIG. 12 is a sequence diagram showing signaling indicating updating ofthe active set in the radio communications system. Hereafter, exchangeof information among a mobile communications terminal 6, a base station5, and a base station control apparatus 4 will be explained withreference to FIG. 12.

When updating the active set in the above-mentioned way (in step ST61),the mobile communications terminal 6 transmits active set updateinformation indicating that the active set has been updated to the basestation 5 using a RACH which is a common channel (in step ST62).

When receiving the active set update information from the mobilecommunications terminal 6, the base station 5 transmits the active setupdate information to the base station control apparatus 4 (in stepST63).

When receiving the active set update information from the base station5, the base station control apparatus 4 refers to the state of theS-CCPCH of a base station 5 which has been newly included in the activeset (in step ST64). In other words, the base station control apparatuschecks to see whether the base station 5 newly included in the activeset is currently carrying out a multimedia service.

When determining that the base station 5 newly included in the activeset is not currently carrying out any multimedia service, the basestation control apparatus instructs the base station 5 to startperforming a multimedia service (in step ST66).

The base station control apparatus 4 then acquires S-CCPCH parameters(e.g., timing, a code, etc.) and information about the state of theservice being started, and starts RRC (Radio Resource Control) signaling(in step ST67).

The base station 5 receives the S-CCPCH parameters from the base stationcontrol apparatus 4, and carries out signaling transmission of theS-CCPCH parameters using, for example, a CPICH which is a common channel(in step ST68).

When carrying out signaling reception of the S-CCPCH parameters from thebase station 5 (in step ST69), the mobile communications terminal 6 setsthe S-CCPCH parameters so as to carry out a process of receiving data(in step ST70).

As can be seen from the above description, each mobile communicationsterminal in accordance with this embodiment 3 includes an update requestmeans for comparing the reception levels of radio signal transmittedfrom a plurality of base stations 5, and for transmitting a request toupdate the active set according to the result of the comparison.Therefore, the present embodiment offers an advantage of being able tosecure the reception quality of radio signals even if each mobilecommunications terminal 6 moves.

In accordance with this embodiment 3, each mobile communicationsterminal 6 transmits a request to update the active set to a basestation 5, as previously mentioned. When a dedicated channel has beenestablished with the base station 5, each mobile communications terminal6 can apply an active set of dedicated channels to common channels, and,in this case, does not need to transmit a request to update the activeset to any base station 5.

Embodiment 4

In accordance with above-mentioned embodiment 3, each mobilecommunications terminal 6 compares the reception levels of radio signalstransmitted from a plurality of base stations 5, and transmits a requestto update the active set to a base station 5 according to the result ofthe comparison, as previously explained. Each mobile communicationsterminal 6 can alternatively include a monitor target updating meansfor, when updating the active set, receiving required broadcastinformation from a base station 5, and for referring to the broadcastinformation to update the active set, thereby eliminating theparticipation of base stations 5 in the updating of the active set. Thesearch unit 15 and protocol control unit 26 of FIG. 2 constitute themonitor target updating means.

FIG. 13 is a sequence diagram showing parameter information when theradio communications system of this embodiment updates the active set.

First, a base station control apparatus 4 transmits, as broadcastinformation, information (e.g., a threshold) required for the updatingof the active set to corresponding base stations 5 (in step ST71).

When receiving the broadcast information from a base station controlapparatus 4, the base station 5 transmits the broadcast information tomobile communications terminals 6 (in step ST72).

When receiving the broadcast information from the base station 5 (instep ST73), the mobile communications terminal 6 refers to the broadcastinformation and then sets the information (e.g., the threshold) requiredfor the updating of the active set (in step ST73).

The base station control apparatus 4 refers to the states of theS-CCPCHs (e.g., service conditions and timing) of neighboring basestations after transmitting the broadcast information to base stations 5(in step ST75).

The base station control apparatus 4 then assembles, as informationelements, S-CCPCH parameters (in step ST76), and transmits, as broadcastinformation, the S-CCPCH information elements to base stations 5 (instep ST77).

When receiving the broadcast information from the base station controlapparatus 4, the base station 5 transmits the broadcast information tomobile communications terminals 6 (in step ST78).

When receiving the broadcast information from the base station 5 (instep ST79), each mobile communications terminal 6 refers to thebroadcast information to set the S-CCPCH parameters and starts receptionof data (in step ST80).

FIG. 14 is a flow chart showing a process of updating the active setcarried out by each mobile communications terminal 6. However, since aprocess of adding a base station into the active set, a process ofreplacing a base station of the active set with another base station,and a process of deleting a base station from the active set of eachmobile communications terminal 6 are the same as those of FIG. 11, theexplanation of them will be omitted hereafter.

The Process of Adding a Base Station into the Active Set

The protocol processing unit 26 of each mobile communications terminal 6receives the S-CCPCH parameters (including the state of services usingthe S-CCPCH) as broadcast information from a base station 5 (in stepST81).

-   The protocol processing unit 26 then refers to the state of services    using the S-CCPCH included in the S-CCPCH parameters to check to see    whether the base station 5 corresponding to the S-CCPCH parameters    is currently performing a service (in step ST82).

When the base station 5 corresponding to the S-CCPCH parameters iscurrently performing a service, the protocol processing unit 26 adds thebase station 5 to the active set (in step ST83).

The protocol processing unit 26 also notifies the S-CCPCH parameters tothe search unit 15, finger assignment control unit 17, and RAKEcombining unit 18.

After that, each mobile communications terminal starts a process ofreceiving data associated with the S-CCPCHs of the base stations 5included in the active set including the added base station 5 (in stepST84).

The Process of Replacing a Base Station of the Active Set with AnotherBase Station

The protocol processing unit 26 receives, as broadcast information, theS-CCPCH parameters (including the state of services using the S-CCPCH)from a base station 5 (in step ST85).

The protocol processing unit 26 then refers to the state of servicesusing the S-CCPCH included in the S-CCPCH parameters to check to seewhether the base station 5 corresponding to the S-CCPCH parameters iscurrently performing a service (in step ST86).

When the base station 5 corresponding to the S-CCPCH parameters iscurrently performing a service, the protocol processing unit 26 excludesa base station 5 having the lowest reception level from the basestations 5 included in the current active set (in step ST87).

The protocol processing unit 26 then adds the base station 5corresponding to the S-CCPCH parameters to the active set (in stepST88).

The protocol processing unit 26 also notifies the S-CCPCH parameters tothe search unit 15, finger assignment control unit 17, and RAKEcombining unit 18.

After that, each mobile communications terminal starts a process ofreceiving data associated with the S-CCPCHs of the base stations 5included in the active set including the base station 5 which is addedto the active set in place of the excluded base station (in step ST89).

The Process of Deleting a Base Station from the Active Set

The protocol processing unit 26 stops the process of receiving dataassociated with the S-CCPCH of a base station 5 having the lowestreception level which is included in the base stations 5 of the currentactive set (in step ST90), and excludes the base station 5 from theactive set (in step ST91).

As can be seen from the above description, in accordance with thisembodiment 4, each mobile communications terminal 6 is so constructed asto, when updating the active set, receive required broadcast informationfrom a base station 5 and refer to the broadcast information to updatethe active set. Therefore, the present embodiment offers an advantage ofbeing able to secure the reception quality of radio signals even if eachmobile communications terminal 6 moves.

In accordance with this embodiment 4, each mobile communicationsterminal 6 does not need to transmit a request to update the active setto a base station 5, unlike that of above-mentioned embodiment 3.Therefore, the present embodiment offers another advantage of making itpossible for each mobile communications terminal to carry out theprocess of updating the active set more promptly than that ofabove-mentioned embodiment 3.

While the radio communications system of this embodiment can broadcastinformation about S-CCPCHs to a plurality of mobile communicationsterminals 6 at a time, each mobile communications terminal does not needto notify information including information about the process of addingabase station to the active set to base stations 5. Therefore, thepresent embodiment offers a further advantage of being able to reducethe number of times that signaling is performed when a large number ofmobile communications terminals 6 are staying in the coverage area ofeach base station.

Embodiment 5

In accordance with above-mentioned embodiment 3, each mobilecommunications terminal 6 compares the reception levels of radio signalstransmitted from a plurality of base stations 5, and transmits a requestto update the active set to a base station 5 according to the result ofthe comparison, as previously explained. When comparing the receptionlevels of radio signals transmitted from a plurality of base stations 5,each mobile communications terminal 6 can estimate the reception levelsof the radio signals as follows.

In other words, in order to check reception power as the reception levelof a radio signal transmitted using an S-CCPCH, each mobilecommunications terminal needs to set a code and timing for the S-CCPCHand demodulate the signal to determine power RSCP assigned to the code.

However, in order to acquire the S-CCPCH parameters in advance and tocarryout set the code for the S-CCPCH, each mobile communicationsterminal needs to carry out complicated processing.

In accordance with this embodiment 5, a base station 5 notifies a ratiobetween the power of a CPICH (i.e., a pilot channel) and that of anS-CCPCH (i.e., a common channel) to a mobile communications terminal 6in advance, and the mobile communications terminal 6 measures the powerof the CPICH and practices the method of estimating the power of theS-CCPCH from the measured power of the CPICH and the above-mentionedratio between the power of the CPICH and that of the S-CCPCH.

To be more specific, the processing is carried out as follows.

FIG. 15 is a sequence diagram showing the notification of the ratiobetween the power of the CPICH and that of the S-CCPCH.

First, a base station control apparatus 4 acquires the ratio between thepower of the CPICH of each base station 5 and that of the S-CCPCH (instep ST101).

The base station control apparatus 4 then transmits, as broadcastinformation, the ratio between the power of the CPICH and that of theS-CCPCH to each base station 5.

When receiving the broadcast information from the base station controlapparatus 4, each base station 5 transmits the broadcast information tomobile communications terminals 6 (in step ST102).

Each mobile communications terminal 6 measures the power of the CPICH ofeach base station 5, and, when receiving the broadcast information froma base station 5 (in step ST103), refers to the broadcast information,and calculates the power of the S-CCPCH by multiplying the power of theCPICH of each base station 5 by the ratio between the power of the CPICHand that of the S-CCPCH (in step ST104).

FIG. 16 is a flow chart showing the process of updating the active setof each mobile communications terminal.

The search unit 15 of each mobile communications terminal 6 receives, asbroadcast information, the ratio between the power of the CPICH of eachbase station 5 and that of the S-CCPCH from a base station 5 (in stepST111).

The search unit 15 measures, as the power of the CPICH of each basestation 5, the reception level of the CPICH of each base station 5 whichis not included in the current active set, as well as the receptionlevel of the CPICH of each base station 5 included in the current activeset (in step ST112).

The search unit 15 then calculates the power of the S-CCPCH of each basestation 5 by multiplying the power of the CPICH of each base station 5by the ratio between the power of the CPICH and that of the S-CCPCH (instep ST113).

The search unit 15 compares the reception levels of the S-CCPCH of thebase stations 5 with one another, and ranks them in order (in stepST114).

The search unit 15 sets the lowest one of the reception levels of theS-CCPCHs of the base stations 5 included in the active set to X, andcalculates an addition threshold Tadd from the lowest S-CCPCH receptionlevel X and a hysteresis parameter H for preventing variations in theactive set.Tadd=X+H/2

In this case, the search unit 15 can receive the addition threshold Taddfrom an upper layer instead of calculating the addition threshold Tadd.

When calculating the addition threshold Tadd in the above-mentioned way,the search unit 15 shifts to the process of step ST24 of FIG. 10. Sincesubsequent processes are the same as those of above-mentioned embodiment1, the explanation of the processes will be omitted hereafter.

As can be seen from the above description, in accordance with thisembodiment 5, each mobile communications terminal is so constructed asto receive information indicating the ratio between the power of theCPICH and that of the S-CCPCH from each of a plurality of base stations6 in advance, and estimates the reception levels of radio signalstransmitted from the plurality of base stations 5 using the S-CCPCHsfrom the reception levels of radio signals transmitted from theplurality of base stations 5 using the CPICHs and the ratio between thepower of the CPICH of each base station and that of the S-CCPCHs.Therefore, the present embodiment offers an advantage of being able toacquire the reception levels of radio signals transmitted from theplurality of base stations 5 using the S-CCPCHs without carrying outcomplicated processing, such as a process of acquiring the S-CCPCHparameters to carry out code setting. The present embodiment is usefulespecially for a case where the transmission levels of the S-CCPCHs varyamong the plurality of base stations 5 since a number of code settingprocesses can be eliminated.

INDUSTRIAL APPLICABILITY

As mentioned above, the radio communications system in accordance withthe present invention is suitable for a case where when a plurality ofbase stations broadcast multimedia data to mobile communicationsterminals using S-CCPCHs, each mobile communications terminal needs toselect a base station from which it can receive the multimedia dataoptimally to improve the reception quality of the multimedia data.

1. A base station which can be used for providing a multimedia broadcastmulticast service (MBMS) of multicasting or broadcasting a multimediadata to a plurality of mobile stations in a communications system, saidbase station comprising: a power ratio transmitting unit fortransmitting together, from one cell, respective information about apower ratio between a power of a common control physical channel usedfor multicasting or broadcasting said multimedia data in each ofneighbor cells and a power of a common pilot channel used fortransmitting an information on reference of timing in each of theneighbor cells; and a service information transmitting unit fortransmitting service information indicating a state of an MBMS servicein said each of the neighbor cells, wherein said base station transmitsthe information about said power ratio and said service information tosaid mobile station in order to enable a mobile station which willreceive the information about said power ratio and said serviceinformation to determine a ranking of a plurality of cells on the basisof the information about said power ratio in each of the neighbor cellsand the power of said common pilot channels, and enable the mobilestation to determine a set including the plurality of cells from which amobile station can receive an MBMS on the basis of the determinedranking and a predetermined threshold, and said service information. 2.A method of operating a base station to provide a multimedia broadcastmulticast service (MBMS) of multicasting or broadcasting a multimediadata to a plurality of mobile stations in a communications system, saidmethod comprising: transmitting together, from one cell, respectiveinformation about a power ratio between a power of a common controlphysical channel used for multicasting or broadcasting said multimediadata in each of neighbor cells and a power of a common pilot channelused for transmitting an information on reference of timing in each ofthe neighbor cells; and transmitting service information indicating astate of an MBMS service in said each of the neighbor cells, wherein thetransmitting the information about said power ratio and said serviceinformation enables a mobile station which will receive the informationabout said power ratio and said service information to determine aranking of a plurality of cells on the basis of the information aboutsaid power ratio in each of the neighbor cells and the power of saidcommon pilot channels, and enable the mobile station to determine a setincluding the plurality of cells from which a mobile station can receivean MBMS on the basis of the determined ranking and a predeterminedthreshold, and said service information.